The invention relates to a jet weaving machine including a monitoring apparatus for weft threads which is arranged on the receiving side.
In jet weaving machines the weft insertion takes place by means of a fluid, which inserts the respective weft thread from the insertion side through the open shed to the receiving side. In air jet weaving machines this fluid, which serves as a transport medium, is air.
For the weft insertion a definite and predeterminable thread length, which is naturally dependent on the weaving width, is drawn off in each case at the insertion side from the stationary winding drum of a thread supply apparatus and supplied to a main nozzle. The main nozzle is fed with compressed air and accelerates the weft thread into the open shed. Usually a plurality of auxiliary or relay nozzles are provided along the weft insertion path, which are likewise fed with compressed air and guide the weft thread through the shed to the receiving side. After the completion of the weft insertion the leading end of the weft thread is captured and held e.g. by a stretching or capture nozzle and the weft thread is beat up to the cloth by the weaving sley. Then the change of shed takes place, through which the weft thread is bound in over the entire weaving width. Then the thread must be severed on the insertion side between the main nozzle and the cloth edge which is near it in order to be ready for the next weft insertion. On the receiving side the inserted weft thread is likewise severed. The superfluous thread remnant is disposed of by means of a suction or blow off device. After the change of shed the end of the inserted weft thread at the receiving side can then be tucked into the following open shed for example by means of a selvedge tucking apparatus.
To monitor the correct weft insertion it is customary to detect both the arrival of the weft thread, which must take place within a certain time window with respect to the weaving cycle, and to measure the length of the inserted weft thread. If the weft thread does not arrive within the predeterminable time window or if it is detected to be too long, then as a rule corrective measures or even the stopping of the weaving machine are necessary.
In order to monitor both the arrival time as well as the length of the weft thread, sensors, which are designated as weft thread monitors, and which are in each case designed in such a manner that that they can detect the weft thread or the weft thread end respectively, are provided at the receiving side. The first weft thread monitor is usually arranged directly at the end of the weft insertion path on the receiving side. It detects whether or not the weft thread end arrives within the predetermined time window—referred to the weaving cycle. However with this one sensor alone it cannot be tested for example whether the inserted weft thread is too long (long weft thread insertion). Therefore a second weft thread monitor is provided, which is usually arranged in such a manner that the weft thread end does not even reach it in the event of a correct weft thread insertion. In the event of a correct weft thread insertion the weft thread end moves up to a position somewhere between the two weft thread monitors, so that the second sensor gives off no signal.
In known jet weaving machines both weft thread monitors are firmly mounted on the weaving sley so that both execute the oscillatory movement synchronously with the weaving sley. For this it is necessary to guide the weft thread between the first and the second weft thread monitors. A known solution consists in providing an auxiliary reed on the weaving sley as a thread guide for bridging the distance between the two weft thread monitors. Auxiliary nozzles are provided along this auxiliary reed for stretching and/or holding the inserted weft thread.
This construction with the auxiliary reed is however relatively complicated and expensive and takes up space in addition. Furthermore, the auxiliary reed has the disadvantage that it represents an additional mass to be accelerated which executes the same oscillatory movement as the weaving sley.